This invention relates to the preparation of 4,4'-dioxy-substituted stilbenes. More specifically, it relates to a dehydrohalogenation-rearrangement of 1,1-bis(4-oxy-substituted aryl)-2-haloethanes under acidic reaction conditions to yield 4,4'-dioxy-substituted stilbenes, particularly 4,4'-dihydroxystilbene from 1,1-bis(4-hydroxyphenyl)-2-chloroethane.
The dehydrohalogenation-rearrangement of 1,1-bis(4-hydroxyaryl)-2-haloethanes to 4,4'-dihydroxystilbenes is known in the art. The reaction is effected under strongly basic and rather drastic conditions by heating the compound in a solution of potassium hydroxide or sodium hydroxide in methanol or ethanol at the boiling point of the solvent, followed by further heating of the dehydrohalogenated product in a high-boiling solvent selected from the group consisting of ethylene glycol, diethylene glycol monomethyl ether (methyl carbitol), and nitrobenzene to the boiling point of such solvent. The reaction may also be effected in one step by heating the 1,1-bis(4-hydroxyaryl)-2-haloethane directly in a solution of potassium hydroxide or sodium hydroxide in a high-boiling solvent selected from the above list. These processes of preparing 4,4'-dihydroxystilbenes are disclosed in Sieber, U.S. Pat. No. 3,624,162. However, they involve the difficult isolation of the desired stilbene from a high-boiling solvent, a factor which significantly decreases the commercial attractiveness and adaptability of the processes.
The disadvantages encountered in the strongly basic, high-boiling solvent processes of the prior art are overcome by the discovery that the dehydrohalogenation-rearrangement of 1,1-bis(4-oxy-substituted aryl)-2-haloethanes can be readily accomplished under acidic reaction conditions to yield 4,4'-dioxy-substituted stibenes.